This invention relates to a low noise solenoid valve. More specifically, the invention is directed to a solenoid valve wherein the noise caused by impact of the armature against the pole piece during opening of the valve, and against the valve seat during closure of the valve is substantially reduced.
It is known in the art to utilize an electric solenoid to open and close a valve by fitting one end of the solenoid armature with a resilient valve member to selectively seal and expose the opening in a valve seat in the path of fluid flow from an inlet port to an outlet port. In a normally closed valve, a return spring biases the armature toward the valve seat so that the valve member is in sealing engagement with the opening in the valve seat when the coil of the solenoid is not energized. Upon energization of the coil, the armature is drawn away from the valve seat to expose its opening and permit fluid flow.
As the armature is drawn away from the valve seat by the magnetic force imparted by the energized coil, it is accelerated toward the pole piece upon which it impacts with an audible "click." Thereafter, while the solenoid remains energized, there is often an audible "hum" while the armature remains in engagement with the pole piece. The hum is usually due to a ripple in the amplitude of the solenoid current waveform which causes the electromagnetic force holding the armature against the pole piece in opposition to the constant force of the return spring to fluctuate.
When the valve is deenergized, the electromagnetic force holding the armature against the pole piece decays and the force of the return spring accelerates the armature toward engagement with the valve seat. Contact of the valve member on the valve seat causes a further sound which may be undesirable.
It is known in the art to reduce valve noise by providing an elastomeric member between the armature and pole piece to absorb the impact which follows energization. This approach is of limited effectiveness in reducing noise during energization and has no effect on valve noise resulting from deenergization.
Another approach taken in the prior art is to employ a movable armature and no pole piece. This technique can be used to prevent contact between the pole piece and armature during energization. However, again, this does nothing to prevent noise following deenergization. Moreover, this technique is magnetically inefficient thereby requiring a larger solenoid to accomplish a given task.